1. Field of the Invention
The present invention relates to the stabilization of polymers. More particularly, the present invention relates to the use of styrenated-p-cresols to stabilize polymeric compositions, preferably compositions comprising thermoplastic polymers or elastomers.
2. Description of Related Art
There is a continuing need for phenolic antioxidants having a liquid physical form in a number of polymer markets, such as thermoplastics, thermoelastomers, rubber, and oil additives. For many phenolic antioxidants, the liquid physical form can only be brought about by heating them to temperatures above their melting points. Examples include octadecyl-3,5-di-tert-butyl-4-hydroxycinnamate, the melting point of which is in the range from between 48° C. and 58° C., and 2,6-di-tert-butyl-p-cresol, whose melting point is approximately 69° C.
A major drawback associated with offering a compound that is solid at room temperature in its molten state, is that, in order to retain it in a liquid physical form, continued heating is required. In the field, however, heating is not always sustainable and, therefore, the molten product may cool and form a solid. Once solidified, it becomes all but impossible to transfer the compound out of its storage container, which may be necessary to convey it to the polymer to be stabilized. On the other hand, returning it to a liquid physical form requires re-heating, but re-melting a solid material in a closed container can be a laborious and drawn out process. Thus, the situation can lead to process delays, thereby adding unnecessary cost.
An additional problem can occur when the polymer employed is a polyurethane, especially foamed polyurethanes, which are commonly made from polyether polyols (polyols) and diisocyanates. The polyol component employed in the manufacture of such polyurethane foams normally contains antioxidants for improved stability and low color. Polyurethane-type foam products are commonly used in automotive interior applications, e.g. seating or dashboards, and there is a growing concern over the level of additives that may be emitted from plastics used in such applications. The phenomenon of additives being emitted from automotive interior plastics is sometimes known as fogging, as volatilized additives are known to deposit themselves on the inside of the windows of the automobile cabin. Once deposited, they may cause the windshield or other windows to fog up. The concern over automotive interior fog, however, is not simply a matter of safety owing to impaired visibility, but, rather, is also fueled by concern for the health of the car's occupants.
Thus, a need exists for the development of antioxidants or stabilizers having two key features for polyol stabilization: first, they must display low fog characteristics compared to industry standard controls, and second, they must either match or exceed the stabilizer efficiency of industry standards.
U.S. Pat. No. 3,956,247 discloses that the solution halogenation of EPDM (rubbery terpolymer of ethylene, an alpha mono-olefin, and a nonconjugated diene) in the presence of an epoxy compound, such as epoxidized soybean oil, with or without a poly(alkylene ether) glycol yields a halogenated EPDM of excellent viscosity stability and limited gel content. A mixture of two parts of nonylated phenyl phosphite and one part of styrenated-p-cresol can be employed as an antioxidant.
U.S. Pat. No. 5,140,055 discloses that a rubber composition containing a specifically limited imidazole compound or imidazoline compound, or benzimidazole or its specifically limited derivative has a large tan δ at high temperature range, and a tire having a tread using such rubber composition is prevented from being lowered in the value of tan δ due to the temperature rising during the running and has an improved grip performance during the high speed running. The use of Bronsted acid in combination with the imidazole, imidazoline or benzimidazole can obviate the drawback of poor scorch resistance of a rubber composition containing the imidazole, imidazoline or benzimidazole alone. The Bronsted acid to be used includes phenol derivatives, carboxylic acids, sulfonic acids, sulfuric acid and its derivatives, phosphoric acid and its derivatives, cyanuric acid and its derivatives, sulfinic acid, nitric acid and its derivatives, phosphorous acid and carbonic acid and its derivatives. Compounds listed as useful include 2,6-di-tert-butyl-p-cresol, 2,2′-methylenebis-4-methyl-6-tert-butylphenol, 4,4′-thiobis-3-methyl-6-tertbutylphenol, styrenated p-cresol, phosphoric acid, phosphoric acid esters, phosphorous acid, and phosphorous acid esters, among many others.
U.S. Pat. No. 5,466,740 discloses a halogen-containing resin composition made stable to heat and light, by incorporating (a) a calcium-based composite metal hydroxide and a calcium-based composite metal oxide, (b) a β-diketone compound or metal salt thereof, and optionally (c) an organic acid salt of zinc. The halogen-containing resin composition may contain conventional additives, such as organic tin stabilizers, epoxy stabilizers, phosphorous acid esters, sulfur-containing compound stabilizers, phenolic stabilizers, and antioxidants, e.g., styrenated p-cresol, 2,6-di-tert-butyl-4-methylphenol, butylated anisol, 4,4′-methylenebis (6-tert-butyl-3-methylphenol), 2,2′-methylenebis (6-tert-butyl-4-methylphenol), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, and tetrakis [3-(4-hydroxy-3,5-di-tert-butylphenyl)propionyloxymethylene]methane.
U.S. Pat. No. 6,242,562 discloses a process for producing a vinyl chloride polymer that includes the steps of: (A) suspension polymerizing vinyl chloride or a monomer mixture containing vinyl chloride, in an aqueous medium to obtain a polymer slurry; (B) stripping unreacted monomers remaining in the polymer slurry; and (C) subjecting the polymer slurry having passed through the step (B), to dehydration at a temperature of from 80° C. to 95° C., preferably within 60 minutes after the stripping. More specifically, first, vinyl chloride or a monomer mixture containing vinyl chloride, an aqueous medium, a polymerization initiator and a dispersant are charged into a polymerization vessel, and a prescribed polymerization temperature (usually from 30 to 75° C.) is maintained with stirring to polymerize the vinyl chloride or the monomer mixture. At the time the polymerization has reached a prescribed degree (usually from 60 to 98%), the polymerization is terminated by, e.g., adding to the reaction mixture an antioxidant having a polymerization inhibitory action, e.g., phenol type antioxidants, such as styrenated p-cresol, among many others.
U.S. Pat. No. 6,339,132 discloses a process for regenerating unreacted vinyl chloride monomers including the step of compressing by means of an compressor an unreacted vinyl chloride monomer recovered from a process of vinyl chloride polymer production; and compressing the same in contact with a lubricating oil fed into the compressor. In this process, the lubricating oil contains a polymerization inhibitor having a polymerization inhibitory action to the vinyl chloride monomer. Such a polymerization inhibitor may be exemplified by phenol type inhibitors, such as styrenated p-cresol, among many others; amine type inhibitors; sulfur type inhibitors; and phosphorus type inhibitors, which can be used singly or in combination of two or more.
U.S. Pat. No. 6,391,065 discloses a water-dilutable UV light absorber composition and method for improving the lightfastness of dyed textiles. The composition is applied to the textiles and includes an ultraviolet light absorbing agent and an organic solvent suitable for dissolving the ultraviolet light absorbing agent. Example 5 of the patent discloses adding 10.0 g of benzyl-benzoate into 20.0 g “Naugard 529” liquid anti-oxidant/solvent (alkylated-styrenated p-cresol) to reduce viscosity.